In the manufacture of many devices, the need exists to lift and rotate the part, for example, in the manufacture of semiconductor devices. A semiconductor wafer is a thin, circular slice of pure silicon on which semiconductors are built. The largest wafer in current use is about 300 mm (12 inches) in diameter. Many individual semiconductor devices or xe2x80x9cchipsxe2x80x9d can be fabricated on each wafer, depending on the chip and wafer size.
For inspection, test or fabrication, a wafer is mounted on a rotating stage that must be capable of orienting the wafer at precise angular positions about an axis perpendicular to the wafer surface. The stage must be rapidly rotated from one position to another. Such stages must also be adjustable in the vertical direction, although only about 10 mm or less of vertical adjustment is needed.
In the past, stages as above described have required complex mechanical components, such as worm gears, lead screws, and separate motors, all of which can be a source of positioning errors. Moreover, these mechanical components resulted in a bulky apparatus having an undesirably large footprint. Other direct drive technologies, such as piezoelectric drives, have limited travel range and require additional mechanical elements to extend their travel range.
It is an object of the present invention to provide a vertical lift and rotation stage without worm gears, lead screws, or separate drive motors.
It is a further object of the present invention to provide a small footprint vertical lift and rotation stage.
Briefly, according to the present invention, a direct drive vertical lift and rotation stage comprises an annular z-axis housing having a central opening and a z-axis rotor assembly journaled by a bearing assembly within the central opening of the z-axis housing. The z-axis rotor assembly has a threaded upper end. A first brushless permanent magnet motor is positioned between the z-axis housing and the z-axis rotor. An annular theta-axis housing has a central opening. The theta-axis housing has threads that engage the threads on the z-axis rotor. Linear bearings between the z-axis housing and the theta-axis housing prevent relative rotation. A theta-axis rotor assembly is journaled by a bearing assembly within the central opening of the theta-axis housing. A second brushless permanent magnet motor is positioned between the theta-axis housing and the theta-axis rotor. A linear position sensor detects vertical movement between the theta-axis housing and the z-axis housing and a rotary sensor detects rotating movement between the theta-axis rotor assembly and the theta-axis housing. The action of the first permanent magnet motor raises and lowers the theta-axis rotor assembly and the action of the second permanent magnet motor rotates the theta-axis rotor assembly.
In one embodiment, the permanent magnet motors comprise armature windings secured to the housing assemblies, rare earth permanent magnets secured to the rotor assemblies, and magnetic metal lamination stacks or steel ring support the armature windings.
The type of the position sensors employed will depend on the motion performance requirement, speed, resolution, accuracy, acceleration, etc. Position sensors, for example, may include incremental or absolute encoders of the magnetic or optical type. Position sensors may also comprise resolvers and related multipole devices.
Stops that limit the rotation of the theta-axis rotor to less than one revolution, home sensors and limit switches to constrain the vertical movement, and rotation of the theta-axis rotor are optional features.